Atlas BT46 Bipod Really Right Stuff BTC-Pro Dual ARCA and Picatinny Mount 5-9 Inches Black. The BT46-NC model Atlas Bipod is part of their PSR Series. The NC stands for No Clamp, meaning it requires any 17S size mount in order to attach to a firearm. The interface to install a clamp uses a two-hole pattern of 1.100 inches with 10-32 threads. It will also mount directly to BT19 AI Spigot or BT70 M-LOK Adapter. The BT46-NC is comprised of 6061-T6 aluminum, except the strengthened inner legs which are made from 7075-T6 aluminum that are Mil-Spec Type III hard coat anodized with heat.